Symptomatic fetal CMV infections occur following a primary maternal infection during pregnancy. We have recently proven that children attending day care centers (DCCs) rapidly transmit CMV from one to another and then transmit the virus to their mothers. However, the relative risk for CMV acquisition by personnel caring for young children in DCCs and by the mothers of these children is unknown. Using the techniques for the rapid analysis of CMV DNA that we have developed as an epidemiologic tool, we will determine the precise risk to women for CMV acquisition from infected children and study the transmission of CMV from child to child, from children to their families, and within families. We will study 3 DCCs enrolling approximately 200 children. A control group of 200 families having children between 0 and 5 years of age not attending DDCs will also be studied. Each child and family member will be surveyed for CMV infections at 2 to 3 month intervals by testing for IgG and IgM antibodies to CMV, and by quantitative CMV viral cultures. The DNA of each CMV isolate will be analyzed by restriction endonucleases using both in vitro labelling and in situ hybridization. These two methods will be compared for their ability to detect epidemiologically important differences. We will assess whether seropositive individuals become infected with exogenous strains and transmit virus to others. We will determine whether an individual is most contagious during the acute or chronic stages of a primary infection. We will survey 400 children 5 to 10 years of age, cohorted by classroom, for the prevalence of viral excretion and using CMV DNA analysis determine if these children transmit CMV among themselves. We will thus establish if DCC attendance by children results in an increased rate of CMV acquisition by mothers and care takers and if this is likely to increase the incidence of symptomatic congenital infections. If so, the prevention of fetal CMV disease may be possible either by interrupting CMV transmission, monitoring high risk women for CMV acquisition during pregnancy, or by using a CMV vaccine.